This invention relates to an apparatus of measuring particulate size without actually contacting the particulate and more particularly to a new apparatus for measuring the size of a particulate simply and rapidly based on interference fringes generated at striped gaps corresponding to the size of the particulate, when a monochromatic beam is radiated on the particulate. By using this invention, improved quality control is available for ceramic powders, magnetic recording material powders and also powder metallurgy and, moreover, it is possible to measure the size of solid state powders as well as liquid state powders, which benefits largely the industrial world.
As well known, about 200 years ago, Thomas Young advanced a theory that interference fringes can be observed at equivalent gaps and in a concentric condition caused by secondary spherical waves originating from the boundary of a subject when a beam is radiated on a subject. At that time, however, interference fringes were not obtained correctly at equivalent gaps, even when experiments were conducted based on the theory of Thomas Young, and therefore his theory was originally concluded to be in error. Thereafter, Young's theory was studied by many scholars, and finally it came to be recognized as a correct theory. However, up to now actual experiments applying the above theory have not been successful.
In view of this situation, the present inventor has performed various experiments, in a trial and error manner, in order to prove Young's theory. As a result, the inventor has found that the interference fringes appear in "shade portions" at equivalent gaps and in a concentric condition when a monochromatic beam is radiated on a particulate having a size in the range of, e.g., 100.about.1000 micrometers. "Shade portions" means a region which is created behind the subject on the opposite side from the light source. This region can also be called a "Geometrical Shadow Region" and is illustrated in FIG. 4.
Further, he has developed the formula mentioned below based on four elements--a gap of interference fringes (.DELTA.x), wavelength of monochromatic beam (.lambda.), size (D) of a particulate, and the distance (Z) between the particulate and a place (e.g., screen) where the interference fringe is measured: ##EQU1##
From the above formula, the size (D) of the particulate is obtainable through the derived formula below: ##EQU2##
This invention utilizes the above-described discoveries for measuring the size of a particulate.
Thus the present invention has an object to provide a new apparatus, by which correct and rapid measuring of particulate size is available without any actual physical contact of the particulate.
The invention has another object to provide a new apparatus to obtain a value for a size of very tiny particulates, even within a range of a few micrometers.
This invention has an even further object to provide a new apparatus to improve quality control for various powder materials such as ceramic powders and so on.
Other objects and advantages of the instant invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.